Dual cavity, high-heat dissipating printed wiring board assembly

ABSTRACT

Two panel-sized fully populated printed wiring board assemblies formed together, with an anisotropic epoxy that provides electrical connection for RF signals and DC supplies without the need for wirebonds, mechanical interconnects or solder balls.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 11/567,906,filed on Dec. 7, 2006, now U.S. Pat. No. 7,444,737, the entire contentsof which are hereby incorporated by reference.

BACKGROUND

1. Field of the Invention

This invention is directed to printed wiring board assemblies and moreparticularly, to a high-heat dissipating RF antenna assembly using aprinted wiring board.

2. Related Art

The constant demand for faster communication systems and more sensitiveradar systems is pushing the phased array industry to move designs toaccommodate higher power levels and higher frequencies. This demandmakes it difficult to produce phased arrays inexpensively and compactly.For low-power, low-frequency applications, Chip-on-Board (COB)technology provides an affordable solution. However, for high-powerphased arrays, which are critical components of high-speed long-rangecommunications and state of art radar applications, COB technology canno longer provide a satisfactory solution due to its limited powerhandling capability. The limiting factor for highly sensitive radars andlong-range communications antenna systems is their higher power outputrequirements. Typically, to deliver the required power, traditionalantenna systems rely on using exotic ceramic materials and complexmulti-part assemblies. These materials are also expensive and requirelong manufacturing lead times.

Therefore, what is needed is an apparatus and associated method thatallows the manufacture of low cost high-heat dissipating phased arrayassembly.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a method for manufacturing dualcavity, high-heat dissipating printed wiring board assembly is provided.This method for manufacturing the printed wiring board comprises:providing a first laminate stackup and a second laminate stackup, havinga plurality of conductive and dielectric layers, including vias withineach stackup, cutouts and alignment holes through each stackup;attaching a heatsink and standoffs to the first stackup; routing out ananisotropic conductive film (ACF) sheet; placing and aligning the ACFsheet over the lower stackup; inverting and assembling upper stackuponto lower stackup; and curing the ACF to join the stackups together.

In another aspect of the present invention, a structure for a dualcavity, high-heat dissipating printed wiring board assembly is provided.The structure for the printed wiring board assembly comprises: an upperand a lower laminate stackup, each having a first side and a secondside, and at least one cutout area, wherein the cutout area of the upperstackup extending from the first side to the second side of the stackup;an anisotropic material layer disposed between the two stackupsproviding mechanical and electrical connection between the stackups; anda heatsink laminated to the upper stackup.

This brief summary has been provided so that the nature of thedisclosure may be understood quickly. A more complete understanding ofthe invention may be obtained by reference to the following detaileddescription of embodiments thereof in connection with the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features and other features of the present disclosure willnow be described with reference to the drawings. In the drawings, thesame components have the same reference numerals. The illustratedembodiment is intended to illustrate, but not to limit the invention.The drawings include the following Figures:

FIG. 1 is a simplified cross sectional view of a conventional COBpackage for an RF antenna application;

FIG. 2 shows a simplified cross sectional view of a dual cavity highheat dissipating printed wiring board assembly, in accordance with anembodiment of the present disclosure;

FIG. 3A shows a simplified cross sectional view of a unit cell of a RFantenna assembly using a dual cavity high heat dissipating printedwiring board, in accordance with an embodiment of the presentdisclosure;

FIGS. 3B and 3C show a simplified bottom view of an upper and top viewof a lower board of a 16 cell RF antenna assembly, in accordance with anembodiment of the present disclosure; and

FIG. 4 is a flowchart showing a method of producing a dual cavity highheat dissipating printed wiring board assembly in accordance with anembodiment of the present disclosure.

DETAILED DESCRIPTION Definitions

The following definitions are provided as they are typically (but notexclusively) used in relation to printed wiring board technology,referred to in various aspects of the present disclosure.

A “stackup” is an arrangement of various layers of conductive anddielectric materials stacked together to form a multi-layer board.

A “laminate” is a structure used to unite conductive and dielectriclayers together.

A “honeycomb” is a circular cell configuration including the antennaradiating aperture, which in the present application permits RFtransmission from the printed wiring board to free-space while alsoacting as the front face of the antenna enclosure.

To facilitate an understanding of the embodiments of the presentdisclosure, the general architecture and the process of making a printedwiring board assembly suitable for RF antenna applications aredescribed. The specific architecture and process of the presentinvention are described with reference to the general architecture andprocess.

FIG. 1 is a simplified cross sectional view of module 100, having atraditional printed wiring board (PWB) 102 with a COB structure 104, aheat sink 110, and a seal ring 112. As shown in FIG. 1, module 100combined together with heat sink 110 and seal ring 112 defines anenclosed space 111. Seal ring 112 is coupled to PWB 102 around aperiphery of ICs or chipset 106. Heatsink 110 is attached to seal ring112 to enclose module 100 and create enclosed space 111. It should beunderstood that each individual module 100 is sealed, even when combinedwith other modules to create large PWBs containing multiple sites.

A number of ICs or chipsets 106, such as ASICs and a MMICs are enclosedin enclosed space 111 between PWB 102 and heat sink 110 and encircled byseal ring 112. In this example, ICs 106 are disposed horizontally on PWB102 alongside one another inside enclosed space 111. The ICs 106 areelectrically coupled together using PWB 102 and a plurality of wirebonds114. Generally, module 100 is not suitable for high power applications,because its heat evacuation capability is limited, primarily since ICs106 are not in direct contact with heatsink 110.

FIG. 2 shows a cross sectional view of a dual cavity high heatdissipating PWB assembly 200 (hereinafter “assembly 200”) in accordancewith an embodiment of the present disclosure. In this embodiment,assembly 200 includes a first PWB assembly 202 and a second PWB assembly206 formed to define an enclosed space 213. As described below, enclosedspace 213 results from the joining of the two fully assembled PWBassemblies 202 and 206, using a conductive epoxy 204, such asAnisotropic Conductive Film sheet (hereinafter “ACF 204”). ACF sheet 204provides a connection for RF and DC signals, without the need for otherinterconnect means, such as wirebonds, mechanical interconnects orsolder balls.

In one embodiment, first PWB assembly 202 is designed to providesuperior heat dissipation for high power ICs. In this embodiment, firstPWB assembly 202 includes; a multilayer stackup 203, a heatsink 208, anda standoff 210. Stackup 203 includes a cutout portion 220 and hasheatsink 208 laminated on its top side. Standoff 210 is disposed insidecutout portion 220 and is attached to heatsink 208. Standoff 210 may beused to elevate high power ICs, such as IC 212, to bonding-pedestal 218and provides a heat conduction path from IC 212 to heatsink 208.

In one embodiment, the structure of second PWB assembly 206 includes atraditional COB structure, the nature of which is known in the art. Inthis embodiment, ICs 214 and 216 are disposed horizontally alongside oneanother in enclosed cutout portion 222.

As understood from FIG. 2, first PWB assembly 202 and second PWBassembly 206 are joined such that cutout portions 220 and 222 arecombined to define and create enclosed space 213, in which ICs 212, 214and 216 are disposed. FIGS. 3A, 3B and 3C show three different views ofa high power RF antenna assembly 300 (hereinafter “assembly 300”). FIG.3A shows a cross sectional view of a unit area of assembly 300. FIG. 3Bshows the bottom side's view of an upper printed wiring board assembly302B and FIG. 3C shows the top side's view of a lower printed wiringboard assembly 302C.

Assembly 300 includes, precut ACF sheet 304 interposed between fullypopulated assembly 300B (FIG. 3B) and fully populated assembly 300C(FIG. 3C). ACF sheet 304 joins assemblies 300B and 300C togethermechanically as well as electrically. ACF sheet 304 provides RF and DCsignal connection without the need for other interconnection means, suchas wirebonds, mechanical interconnects or solder balls.

Assembly 300 further includes a plurality of antenna aperture structures330 imbedded in a honeycomb structure 328, and attached to a bottom sideof assembly 300C. In one embodiment, a pair of alignment holes 332 andalignment pins (not shown), are disposed in at least one corner ofassembly 300 to ensure a proper corresponding alignment of theassemblies.

Assembly 300B (FIG. 3B) includes; multilayer stackup 302, heatsink 308,standoff 310 and IC 312, such as a high power MMIC. Stackup 302 includescutout portion 321 and has heatsink 308 laminated on a first side 309. Astandoff 310 is disposed inside cutout portion 321 and is coupled toheatsink 308. Standoff 310, which may be made from any heat conductivematerial, such as Molybdenum, elevates IC 312 to wirebonding-pedestal318 and provides heat conduction from IC 312 to heatsink 308. IC 312 iswirebonded to stackup 302 at wirebonding-pedestal 318.

Disposed on the bottom side of stackup 302 are arrays of transitionpoints 334 and 336, which provide transition points for RF signals andDC supplies, respectively. Transition points 334 and 336 are thelocations where AFC sheet 304 establishes electrical contact betweenassemblies 300B and 300C.

Assembly 300C (FIG. 3C) includes a multilayer stackup 306, and aplurality of ICs 314 and 316, such as ASICs and MMICs, respectively.Stackup 306 has cutout portion 320 in which ICs 314 and 316 may bepositioned. For example, at cutout portion 320 ICs 314 316 may bephysically coupled to stackup 306 and electrically connected to it with,for example, wirebonds. Disposed on the top side of stackup 306 arearrays of transition points 334 and 336.

In one embodiment, multilayer stackups 302 and 306 may be constructedfrom double-sided RF grade laminate material.

FIG. 4 is a flowchart, illustrating a method 400 for producing a dualcavity, high-heat dissipating PWB assembly, according to one aspect ofthe present disclosure.

Referring now to FIGS. 3A and 4, in step S402, multilayer stackups 302and 304 are provided. Stackups 302 and 304 are pre-routed in apredefined area to form cutout portions 320 and 321.

In step S404, heatsink 308 is laminated onto stackup 302 and standoff310 is attached to heatsink 308.

In step S406, stackups 302 and 306 are populated with ICs 312, 314 and316. In one embodiment, ICs 314 and 316 are positioned within cutoutportion 320 of stackup 306, while IC 312 is positioned on standoff 310.

In step S408, ACF sheet 304 is routed to remove portions of ACF sheet304, which overlay and correspond to cutout portions 320 and 321 andalignment holes 332.

In step S410, alignment pins (not shown) are inserted into assembly 300Cin alignment holes 332. ACF sheet 304 is then aligned and placed overassembly 300C (FIG. 3C).

In step S412, assembly 300B (FIG. 3B) is inverted, aligned, anddeposited onto the ACF covered assembly 300C. The combination ofassembly 300B and assembly 300C to form assembly 300 define and createenclosed space 319. As a result of the combination, ICs 312, 314 and 316are positioned and enclosed within enclosed space 319.

In step S414, assemblies 300B and 300C are pressed together, while ACFsheet 304 is cured under pressure at a predetermined temperature.

In one embodiment, thereafter, a plurality of antenna apertures 330 areimbedded in a honeycomb structure 328 and are attached to a bottom sideof assembly 300C to form assembly 300.

The embodiments disclosed provide a packaging structure and method,which allows for a higher operating frequency, and higher power output.Packaging density may be doubled, while assembly complexity andmanufacturing costs may be reduced and system reliability may beenhanced. The packaging structure also allows for building panel sizedPWB assemblies.

Although the present technology has been described with reference tospecific embodiments, these embodiments are illustrative only and notlimiting. Many other applications and embodiments of the presentdisclosure will be apparent in light of this disclosure and thefollowing claims.

What is claimed is:
 1. A structure for a printed wiring board assemblycomprising: a first laminate stackup, having a first side and a secondside, and a first cutout area defined on the first side of the firstlaminate stackup, wherein the first cutout area does not extend to thesecond side of the first laminate stackup; a second laminate stackup,having a first side and a second side, and a second cutout areaextending from the first side to the second side of the second laminatestackup, wherein the first side of the first laminate stackup isconnected to the first side of the second laminate stackup with thefirst cutout area aligned with the second cutout area; an anisotropicmaterial layer disposed between the first laminate stackup and thesecond laminate stackup providing mechanical and electrical connectiontherebetween; a heatsink, having a first side and a second side,laminated to the second side of the second laminate stackup andextending across the second cutout area, wherein the first laminatestackup, the second laminate stackup, and the first side of the heatsinkdefine an enclosed space including the first cutout area and the secondcutout area; a first integrated circuit attached to the first laminatestackup in the first cutout area; and a second integrated circuitattached to the first side of the heatsink in the enclosed space.
 2. Thestructure of claim 1, wherein the first laminate stackup and the secondlaminate stackup comprise double-sided printed wiring boards havingconductive traces.
 3. The structure of claim 1, wherein layers of thefirst laminate stackup and the second laminate stackup facing theanisotropic material layer include transition points to make electricalconnection with the anisotropic material layer.
 4. The structure ofclaim 1, wherein the first laminate stackup and the second laminatestackup comprise RF grade material.
 5. The structure of claim 1, whereinthe heatsink comprises at least one thermally conductive standoffbetween the heatsink and the second integrated circuit.
 6. The structureof claim 5, wherein the at least one thermally conductive standoff holdsand elevates the second integrated circuit to a wirebonding layer, andprovides heat conduction between the second integrated circuit and theheatsink.
 7. The structure of claim 5, wherein the at least onethermally conductive standoff comprises molybdenum.
 8. The structure ofclaim 1, further comprising an antenna aperture structure attached tothe second side of the first laminate stackup and aligned with theenclosed space.
 9. The structure of claim 8, wherein the antennaaperture structure is embedding in an honeycomb structure.